Update from a select postgres

With the help of this syntax, the join condition is defined between the target and source table. In this last line of the query, we chose the manipulation method for the matched rows. Finally, we added the semicolon ; sign because the MERGE statements must end with the semicolon signs. The major characteristic of the subquery is, they can only be executed with the external query. The noticeable difference in this method is, it might be a convenient way to update one column for the tables that have a small number of the rows.

Now we will execute the following query and then will analyze it. After the execution of the update from a select statement the output of the table will be as below;.

As we can see, the PersonCityName column data of the Persons table have been updated with the City column data of the AddressList table for the matched records for the PersonId column. Regarding this method, we should underline the following significant points. If the subquery finds more than one matched row, the update query will return an error, as shown below:. In this article, we learned to update the data in a table with the data where they are contained in other tables.

PersonId INT. PersonName , PersonLastName. N 'Salvador' , N 'Williams' ,. N 'Lawrence' , N 'Brown' ,. N 'Gilbert' , N 'Jones' ,. N 'Ernest' , N 'Smith' ,. For this purpose, in PostgreSQL there is a mechanism for selecting only rows that are not locked. One thing that we need to keep in mind while working with select for update statements is its effect on foreign keys. When selecting data from the purchases table with select for update , users will be locked as well.

This is necessary because otherwise there is a chance of breaking the foreign-key constraint. In bigger systems, a select for share can have huge negative consequences if it locks a widely used table.

Keep in mind that other processes will only need to wait if they want to update the referenced field. If the other process wants to update some unrelated data, no blocking will occur. A weaker form of select for update is the select for share query. It is an ideal for ensuring referential integrity when creating child records for a parent.

Suppose that we want to create a new purchase for a user. First, we would select the user from the database and then insert a new record in the purchases database. Can we safely insert a new purchase into the database?

See Section 7. The name optionally schema-qualified of the table to update. If ONLY is specified before the table name, matching rows are updated in the named table only. If ONLY is not specified, matching rows are also updated in any tables inheriting from the named table. A substitute name for the target table. When an alias is provided, it completely hides the actual name of the table.

The name of a column in table. The column name can be qualified with a subfield name or array subscript, if needed. An expression to assign to the column. Improve this question. McNets 9, 2 2 gold badges 28 28 silver badges 53 53 bronze badges. What is t. Add a comment. Active Oldest Votes. Improve this answer. Gordon Linoff Gordon Linoff 1. Sign up or log in Sign up using Google.